israel has sealed off the main roads around gaza. will israel invade on the ground? >> i think the chances are going up. >> reporter: jeffrey white, a former analyst with the defense intelligence agency said an israeli ground invasion of gaza would be a brutal, bloody grind. >> there's a high density of population throughout the strip. highest in the major areas, rafa, gaza city, but there are a lot of civilians in other places as well, and the other part is hamas fights from inside the cities. >> cities of narrow streets, bazaars, apartment building. a punishing building to building slog in a place that is slightly twice the size of washington, d.c. we used a googp map with james spider marx. >> what kind of close combat are we talking about? >> this is called combat in restricted terrain. what we have in gaza city, there are about 500,000 people who live in this city. you can only imagine the type of combat that has to take place in this very restricted terrain. >> terrain where marx says israeli troops will be exposed to ambush, sniper fire, suicide bombings. if a